1. Overview

This module implements the TLS transport for Kamailio
using the OpenSSL library
(http://www.openssl.org). To enable the Kamailio TLS support this
module must be loaded and enable_tls=yes core setting
must be added to the Kamailio config file.

IMPORTANT: the tls module must be loaded before any other Kamailio module
that uses libssl (OpenSSL library). A safe option is to have the tls module
loaded first (be in the first "loadmodule" in Kamailio.cfg).

2. Quick Start

Make sure you have a proper certificate and private key and either
use the certificate and private_key
module parameters, or make sure the certificate and key are in the same PEM file,
named cert.pem an placed in [your-cfg-install-prefix]/etc/kamailio/.
Don't forget to load the tls module and to enable TLS
(add enable_tls=yes to your config).

3. Important Notes

The TLS module needs some special options enabled when compiling
Kamailio. These options are enabled by default, however in case
you're using a modified Kamailio version or Makefile, make sure
that you enable -DUSE_TLS and -DTLS_HOOKS (or compile with make
TLS_HOOKS=1 which will take care of both options).

To quickly check if your Kamailio version was compiled with these
options, run kamailio -V and look for USE_TLS and TLS_HOOKS among the flags.

This module includes several workarounds for various Openssl bugs
(like compression and Kerberos using the wrong memory allocations
functions, low memory problems a.s.o). On startup it will try to enable
the needed workarounds based on the OpenSSL library version. Each time
a known problem is detected and a workaround is enabled, a message will
be logged. In general it is recommended to compile this module on the
same machine or a similar machine to where kamailio will be run or to
link it statically with libssl. For example if on
the compile machine OpenSSL does not have the Kerberos support enabled,
but on the target machine a Kerberos enabled OpenSSL library is installed,
Kamailio cannot apply the needed workarounds and will refuse to start.
The same thing will happen if the OpenSSL versions are too different
(to force Kamailio startup anyway, see the tls_force_run
module parameter).

Compression is fully supported if you have a new enough OpenSSL version
(starting with 0.9.8). Although there are some problems with zlib compression
in currently deployed OpenSSL versions (up to and including 0.9.8d, see
openssl bug #1468), the TLS module will automatically switch to its own fixed version.
Note however that starting with Kamailio 3.1 compression is not enabled by
default, due to the huge extra memory consumption that it causes (about 10x
more memory). To enable it use
modparam("tls", "tls_disable_compression", 0)
(see tls_disable_compression).

The TLS module includes workarounds for the following known openssl bugs:

openssl #1204 (disable SS_OP_TLS_BLOCK_PADDING_BUG if compression is enabled,
for versions between 0.9.8 and 0.9.8c),

openssl #1468 (fix zlib compression memory allocation),

openssl #1467 (kerberos support will be disabled if the openssl version is less than 0.9.8e-beta1)

openssl #1491 (stop using tls in low memory situations due to the very high risk of openssl crashing or leaking memory).

4. Compiling the TLS Module

In most case compiling the TLS module is as simple as:

make -C modules/tls

or

make modules modules=modules/tls

or (compiling whole Kamailio and the tls module)

make all include_modules=tls

.

However in some cases the OpenSSL library requires linking with other libraries.
For example compiling the OpenSSL library with Kerberos and zlib-shared support
will require linking the TLS module with libkrb5 and libz. In this case just add
TLS_EXTRA_LIBS="library list" to make's command line. E.g.:

make TLS_EXTRA_LIBS="-lkrb5 -lz" all include_modules=tls

In general, if Kamailio fails to start with a symbol not found error when trying
to load the TLS module (check the log), it means some needed library was not
linked and it must be added to TLS_EXTRA_LIBS

5. TLS and Low Memory

The Openssl library doesn't handle low memory situations very well. If memory
allocations start to fail (due to memory shortage), Openssl can crash or cause memory
leaks (making the memory shortage even worse). As of this writing all Openssl versions
were affected (including 0.9.8e), see Openssl bug #1491. The TLS module has some
workarounds for preventing this problem (see low_mem_treshold1
and low_mem_threshold2), however starting Kamailio with enough shared
memory is higly recommended. When this is not possible a quick way to significantly
reduce Openssl memory usage it to disable compression (see tls_disable_compression).

6. TLS Debugging

Debugging messages can be selectively enabled by recompiling
the TLS module with a combination of the following defines:

TLS_WR_DEBUG - debug messages for the write/send part.

TLS_RD_DEBUG - debug messages for the read/receive
part.

TLS_BIO_DEBUG - debug messages for the custom BIO.

Example 1.2. Compiling TLS with Debug Messages

make -C modules/tls extra_defs="-DTLS_WR_DEBUG -DTLS_RD_DEBUG"

To change the level at which the debug messages are logged,
change the tls_debug module parameter.

7. Known Limitations

The private key must not be encrypted (Kamailio cannot ask you for a password on startup).

The TLS certificate verifications ignores the certificate name, Subject Altname
and IP extensions, it just checks if the certificate is signed by a recognized CA.
One can use the select framework to try to overcome this limitation (check in the
script for the contents of various certificate fields), but this is not only slow,
but also not exactly standard conforming (the verification should happen during TLS
connection establishment and not after).

TLS specific config reloading is not safe, so for now better don't use it,
especially under heavy traffic.

8. Quick Certificate Howto

There are various ways to create, sign certificates and manage small CAs (Certificate Authorities).
If you are in a hurry and everything you have are the installed OpenSSL libraries and utilities, read on.

Assumptions: we run our own CA.

Warning: in this example no key is encrypted. The client and server private keys must not be encrypted
(Kamailio doesn't support encrypted keys), so make sure the corresponding files are readable only by
trusted people. You should use a password to protect your CA private key.

Assumptions
------------
The default openssl configuration (usually /etc/ssl/openssl.cnf)
default_ca section is the one distributed with openssl and uses the default
directories:
...
default_ca = CA_default # The default ca section
[ CA_default ]
dir = ./demoCA # Where everything is kept
certs = $dir/certs # Where the issued certs are kept
crl_dir = $dir/crl # Where the issued crl are kept
database = $dir/index.txt # database index file.
#unique_subject = no # Set to 'no' to allow creation of
# several certificates with same subject.
new_certs_dir = $dir/newcerts # default place for new certs.
certificate = $dir/cacert.pem # The CA certificate
serial = $dir/serial # The current serial number
crlnumber = $dir/crlnumber # the current CRL number
crl = $dir/crl.pem # The current CRL
private_key = $dir/private/cakey.pem# The private key
RANDFILE = $dir/private/.rand # private random number file
...
If this is not the case create a new OpenSSL config file that uses the above
paths for the default CA and add to all the openssl commands:
-config filename. E.g.:
openssl ca -config my_openssl.cnf -in kamailio1_cert_req.pem -out kamailio1_cert.pem
Creating the CA certificate
---------------------------
1. Create the CA directory
mkdir ca
cd ca
2. Create the CA directory structure and files (see ca(1))
mkdir demoCA #default CA name, edit /etc/ssl/openssl.cnf
mkdir demoCA/private
mkdir demoCA/newcerts
touch demoCA/index.txt
echo 01 >demoCA/serial
echo 01 >demoCA/crlnumber
2. Create CA private key
openssl genrsa -out demoCA/private/cakey.pem 2048
chmod 600 demoCA/private/cakey.pem
3. Create CA self-signed certificate
openssl req -out demoCA/cacert.pem -x509 -new -key demoCA/private/cakey.pem
Creating a server/client TLS certificate
----------------------------------------
1. Create a certificate request (and its private key in privkey.pem)
openssl req -out kamailio1_cert_req.pem -new -nodes
WARNING: the organization name should be the same as in the CA certificate.
2. Sign it with the CA certificate
openssl ca -in kamailio1_cert_req.pem -out kamailio1_cert.pem
3. Copy kamailio1_cert.pem to your Kamailio configuration dir
Setting Kamailio to use the TLS certificate
---------------------------------------------
1. Create the CA list file:
for each of your CA certificates that you intend to use do:
cat cacert.pem >>calist.pem
2. Copy your Kamailio certificate, private key and ca list file to your
intended machine (preferably in your Kamailio configuration directory,
this is the default place Kamailio searches for).
3. Set up Kamailio.cfg to use the certificate
if your Kamailio certificate name is different from cert.pem or it is not
placed in Kamailio cfg. directory, add to your kamailio.cfg:
modparam("tls", "certificate", "/path/cert_file_name")
4. Set up Kamailio to use the private key
if your private key is not contained in the same file as the certificate
(or the certificate name is not the default cert.pem), add to your
Kamailio.cfg:
modparam("tls", "private_key", "/path/private_key_file")
5. Set up Kamailio to use the CA list (optional)
The CA list is not used for your server certificate - it's used to approve other servers
and clients connecting to your server with a client certificate or for approving
a certificate used by a server your server connects to.
add to your Kamailio.cfg:
modparam("tls", "ca_list", "/path/ca_list_file")
6. Set up TLS authentication options:
modparam("tls", "verify_certificate", 1)
modparam("tls", "require_certificate", 1)
(for more information see the module parameters documentation)
Revoking a certificate and using a CRL
--------------------------------------
1. Revoking a certificate:
openssl ca -revoke bad_cert.pem
2. Generate/update the certificate revocation list:
openssl ca -gencrl -out my_crl.pem
3. Copy my_crl.pem to your Kamailio config. dir
4. Set up Kamailio to use the CRL:
modparam("tls", "crl", "path/my_crl.pem")

TLSv1 - only TLSv1 (TLSv1.0) connections are
accepted. This is the default value.

SSLv3 - only SSLv3 connections are accepted.
Note: you shouldn't use SSLv3 for anything which should be secure.

SSLv2 - only SSLv2 connections, for old clients.
Note: you shouldn't use SSLv2 for anything which should be secure.
Newer versions of libssl don't include support for it anymore.

SSLv23 - any of the SSLv2, SSLv3 and TLSv1 or
newer methods will be accepted.

From the OpenSSL manual: "A TLS/SSL connection established with these
methods may understand the SSLv3, TLSv1, TLSv1.1 and TLSv1.2 protocols.
If extensions are required (for example server name) a client will
send out TLSv1 client hello messages including extensions and will
indicate that it also understands TLSv1.1, TLSv1.2 and permits a
fallback to SSLv3. A server will support SSLv3, TLSv1, TLSv1.1
and TLSv1.2 protocols. This is the best choice when compatibility
is a concern."

Note: For older libssl version, this option allows SSLv2, with hello
messages done over SSLv2. You shouldn't use SSLv2 or SSLv3 for anything
which should be secure.

If RFC 3261 conformance is desired, at least TLSv1 must be used. For
compatibility with older clients SSLv23 is the option, but again, be aware
of security concerns, SSLv2/3 being considered very insecure by 2014.
For current information about what's considered secure, please consult,
IETF BCP 195, currently RFC 7525 - "Recommendations for Secure Use of
Transport Layer Security (TLS) and Datagram Transport Layer Security (DTLS)"

Example 1.3. Set tls_method parameter

...
modparam("tls", "tls_method", "TLSv1")
...

9.2. certificate (string)

Sets the certificate file name. The certificate file can also contain
the private key in PEM format.

If the file name starts with a '.' the path will be relative to the
working directory (at runtime). If it starts
with a '/' it will be an absolute path and if it starts with anything
else the path will be relative to the main config file directory
(e.g.: for kamailio -f /etc/kamailio/kamailio.cfg it will be relative to /etc/kamailio/).

9.3. private_key (string)

Sets the private key file name. The private key can be in the same
file as the certificate or in a separate file, specified by this
configuration parameter.

If the file name starts with a '.' the path will be relative to the
working directory (at runtime). If it starts
with a '/' it will be an absolute path and if it starts with anything
else the path will be relative to the main config file directory
(e.g.: for kamailio -f /etc/kamailio/kamailio.cfg it will be relative to /etc/kamailio/).

Note: the private key can be contained in the same file as the
certificate (just append it to the certificate file, e.g.:
cat pkey.pem >> cert.pem)

9.4. ca_list (string)

Sets the CA list file name. This file contains a list of all the
trusted CAs certificates used when connecting to other SIP implementations.
If a signature in a certificate chain belongs
to one of the listed CAs, the verification of that certificate will succeed.

If the file name starts with a '.' the path will be relative to the
working directory (at runtime). If it starts
with a '/' it will be an absolute path and if it starts with anything
else the path will be relative to the main config file directory
(e.g.: for kamailio -f /etc/kamailio/kamailio.cfg it will be relative to /etc/kamailio/).

By default the CA file is not set.

An easy way to create the CA list is to append each trusted trusted CA
certificate in the PEM format to one file, e.g.:

for f in trusted_cas/*.pem ; do cat "$f" >> ca_list.pem ; done

See also
verify_certificate,
verify_depth,
require_certificate and
crl.

9.5. crl (string)

Sets the certificate revocation list (CRL) file name. This file contains a
list of revoked certificates. Any attempt to verify a revoked
certificate will fail.

If not set, no CRL list will be used.

If the file name starts with a '.' the path will be relative to the
working directory (at runtime). If it starts
with a '/' it will be an absolute path and if it starts with anything
else the path will be relative to the main config file directory
(e.g.: for kamailio -f /etc/kamailio/kamailio.cfg it will be relative to /etc/kamailio/).

Note

If set, require_certificate should also be set
or it will not have any effect.

By default the CRL file name is not set.

To update the CRL in a running Kamailio, make sure you configure TLS
via a separate TLS config file
(the config modparam) and issue a tls.reload
RPC call, e.g.:

See also
ca_list,
verify_certificate,
verify_depth and
require_certificate.

Example 1.7. Set crl parameter

...
modparam("tls", "crl", "/usr/local/etc/kamailio/crl.pem")
...

9.6. verify_certificate (boolean)

If enabled it will force certificate verification when connecting to
other SIP servers..
For more information see the
verify(1)
OpenSSL man page.

Note: the certificate verification will always fail if the ca_list is empty.

See also: ca_list, require_certificate, verify_depth.

By default the certificate verification is off.

Example 1.8. Set verify_certificate parameter

...
modparam("tls", "verify_certificate", 1)
...

9.7. verify_depth (integer)

Sets how far up the certificate chain will the certificate verification go in the search for a trusted CA.

See also: ca_list, require_certificate, verify_certificate,

The default value is 9.

Example 1.9. Set verify_depth parameter

...
modparam("tls", "verify_depth", 9)
...

9.8. require_certificate (boolean)

When enabled Kamailio will require a certificate from a client
connecting to the TLS port. If the client does not offer a certificate
and verify_certificate is on, certificate verification will fail.

The default value is off.

Example 1.10. Set require_certificate parameter

...
modparam("tls", "require_certificate", 1)
...

9.9. cipher_list (string)

Sets the list of accepted ciphers. The list consists of cipher strings separated by colons.
For more information on the cipher list format see the
cipher(1) OpenSSL man page.

The default value is not set (all the OpenSSL supported ciphers are enabled).

Example 1.11. Set cipher_list parameter

...
modparam("tls", "cipher_list", "HIGH")
...

9.10. server_name (string)

Sets the Server Name Indication (SNI) value.

This is a TLS extension enabling one TLS server to serve multiple host
names with unique certificates.

The default value is empty (not set).

Example 1.12. Set server_name parameter

...
modparam("tls", "server_name", "kamailio.org")
...

9.11. send_timeout (int)

This parameter is obsolete and cannot be used
in newer TLS versions (> Kamailio 3.0). In these versions the
send_timeout is replaced by tcp_send_timeout
(common with all the tcp connections).

9.12. handshake_timeout (int)

This parameter is obsolete and cannot be used
in newer TLS versions (> Kamailio 3.0). In these versions the
handshake_timeout is replaced by tcp_connect_timeout
(common with all the tcp connections).

9.13. connection_timeout (int)

Sets the amount of time after which an idle TLS connection will be
closed, if no I/O ever occurred after the initial open. If an I/O event
occurs, the timeout will be extended with tcp_connection_lifetime.
The value is expressed in seconds.

The default value is 10 min.

If the value set is -1, the connection will never be close on idle.

This setting can be changed also at runtime, via the RPC interface and config
framework. The config variable name is
tls.connection_timeout.

Example 1.13. Set connection_timeout parameter

...
modparam("tls", "connection_timeout", 60)
...

Example 1.14. Set tls.connection_timeout at runtime

$ kamcmd cfg.set_now_int tls connection_timeout 180

9.14. tls_disable_compression (boolean)

If set compression over TLS will be disabled.
Note that compression uses a lot of memory (about 10x more then with
the compression disabled), so if you want to minimize
memory usage is a good idea to disable it. TLS compression also
expose you for the
CRIME security vulnerability.

By default TLS compression is disabled.

Example 1.15. Set tls_disable_compression parameter

...
modparam("tls", "tls_disable_compression", 0) # enable
...

9.15. ssl_release_buffers (integer)

Release internal OpenSSL read or write buffers as soon as they are
no longer needed. Combined with
ssl_freelist_max_len has the potential of saving
a lot of memory ( ~ 32k per connection in the default configuration,
or 16k + ssl_max_send_fragment).
For Kamailio versions > 3.0 it makes little sense to disable it (0)
since the tls module already has its own internal buffering.

A value of -1 would not change this option from its openssl default.
Use 0 or 1 for enable/disable.

By default the value is 1 (enabled).

Note

This option is supported only for
OpenSSL versions >= 1.0.0.
On all the other versions attempting
to change the default will trigger an error.

Example 1.16. Set ssl_release_buffers parameter

modparam("tls", "ssl_release_buffers", 1)

9.16. ssl_freelist_max_len (integer)

Sets the maximum number of free memory chunks, that OpenSSL will keep
per connection. Setting it to 0 would cause any unused memory chunk
to be immediately freed, reducing the memory footprint. A too large
value would result in extra memory consumption.

Should be combined with ssl_release_buffers.

A value of -1 has a special meaning: the OpenSSL default will be used
(no attempt on changing the value will be made). For OpenSSL 1.0
the internal default is 32.

By default the value is 0 (no freelist).

Note

This option is supported only for
OpenSSL versions >= 1.0.0.
On all the other versions attempting
to change the default will trigger an error.

Example 1.17. Set ssl_freelist_max_len parameter

modparam("tls", "ssl_freelist_max_len", 0)

9.17. ssl_max_send_fragment (integer)

Sets the maximum number of bytes (from the clear text) sent into
one TLS record. Valid values are between 512 and 16384.
Note however that even valid low values might not be big enough to
allow a successful handshake (try minimum 1024).

Lower values would lead to less memory usage, but values lower then
the typical Kamailio write size would incur a slight performance
penalty. Good values are bigger then the size of the biggest
SIP packet one normally expects to forward. For example in most
setups 2048 would be a good value.

Note

Values on the lower side, even if valid (> 512), might not allow
for a successful initial handshake. This happens if the
certificate does not fit inside one send fragment.
Values lower then 1024 should not be used.
Even with higher values, if the handshake fails,
try increasing the value.

A value of -1 has a special meaning: the OpenSSL default will be used
(no attempt on changing the value will be made).

By default the value is -1 (the OpenSSL default, which at least in
OpenSSL 1.0.0 is ~ 16k).

Note

This option is supported only for
OpenSSL versions >= 0.9.9.
On all the other versions attempting
to change the default will trigger an error.

Example 1.18. Set ssl_max_send_fragment parameter

modparam("tls", "ssl_max_send_fragment", 4096)

9.18. ssl_read_ahead (boolean)

Enables read ahead, reducing the number of internal OpenSSL BIO read()
calls. This option has only debugging value, in normal circumstances
it should not be changed from the default.

When disabled OpenSSL will make at least 2 BIO read() calls per
received record: one to get the record header and one to get the
rest of the record.

The TLS module buffers internally all read()s and defines its own fast
BIO so enabling this option would only cause more memory consumption
and a minor slow-down (extra memcpy).

A value of -1 has a special meaning: the OpenSSL default will be used
(no attempt on changing the value will be made).

By default the value is 0 (disabled).

Example 1.19. Set ssl_read_ahead parameter

modparam("tls", "ssl_read_ahead", 1)

9.19. send_close_notify (boolean)

Enables/disables sending close notify alerts prior to closing the
corresponding TCP connection. Sending the close notify prior to TCP
shutdown is "nicer" from a TLS point of view, but it has a measurable
performance impact. Default: off. Can be set at runtime
(tls.send_close_notify).

The default value is 0 (off).

It can be changed also at runtime, via the RPC interface and config
framework. The config variable name is tls.send_close_notify.

Example 1.20. Set send_close_notify parameter

...
modparam("tls", "send_close_notify", 1)
...

Example 1.21. Set tls.send_close_notify at runtime

$ kamcmd cfg.set_now_int tls send_close_notify 1

9.20. con_ct_wq_max (integer)

Sets the maximum allowed per connection clear-text send queue size in
bytes. This queue is used when data cannot be encrypted and sent
immediately because of an ongoing TLS level renegotiation.

The default value is 65536 (64 Kb).

It can be changed also at runtime, via the RPC interface and config
framework. The config variable name is tls.con_ct_wq_max.

Example 1.22. Set con_ct_wq_max parameter

...
modparam("tls", "con_ct_wq_max", 1048576)
...

Example 1.23. Set tls.con_ct_wq_max at runtime

$ kamcmd cfg.set_now_int tls con_ct_wq_max 1048576

9.21. ct_wq_max (integer)

Sets the maximum total number of bytes queued in all the clear-text
send queues. These queues are used when data cannot be encrypted and
sent immediately because of an ongoing TLS level renegotiation.

The default value is 10485760 (10 Mb).

It can be changed also at runtime, via the RPC interface and config
framework. The config variable name is tls.ct_wq_max.

9.22. ct_wq_blk_size (integer)

It can be changed also at runtime, via the RPC interface and config
framework. The config variable name is tls.ct_wq_blk_size.

Example 1.26. Set ct_wq_blk_size parameter

...
modparam("tls", "ct_wq_blk_size", 2048)
...

Example 1.27. Set tls.ct_wq_max at runtime

$ kamcmd cfg.set_now_int tls ct_wq_blk_size 2048

9.23. tls_log (int)

Sets the log level at which TLS related messages will be logged.

The default value is 3 (L_DBG).

It can be changed also at runtime, via the RPC interface and config
framework. The config variable name is tls.log.

Example 1.28. Set tls_log parameter

...
# ignore TLS messages if Kamailio is started with debug less than 10
modparam("tls", "tls_log", 10)
...

Example 1.29. Set tls.log at runtime

$ kamcmd cfg.set_now_int tls log 10

9.24. tls_debug (int)

Sets the log level at which TLS debug messages will be logged.
Note that TLS debug messages are enabled only if the TLS module
is compiled with debugging enabled (e.g. -DTLS_WR_DEBUG,
-DTLS_RD_DEBUG or -DTLS_BIO_DEBUG).

The default value is 3 (L_DBG).

It can be changed also at runtime, via the RPC interface and config
framework. The config variable name is tls.debug.

Example 1.30. Set tls_debug parameter

...
# ignore TLS debug messages if Kamailio is started with debug less than 10
modparam("tls", "tls_debug", 10)
...

Example 1.31. Set tls.debug at runtime

$ kamcmd cfg.set_now_int tls debug 10

9.25. low_mem_threshold1 (integer)

Sets the minimal free memory from which attempts to open or accept
new TLS connections will start to fail. The value is expressed in KB.

The default value depends on whether the OpenSSL library used handles
low memory situations in a good way (openssl bug #1491).
As of this writing this is not true for any OpenSSL version (including 0.9.8e).

If an ill-behaved OpenSSL version is detected, a very conservative value is chosen,
which depends on the maximum possible number of simultaneously created TLS connections
(and hence on the process number).

The following values have a special meaning:

-1 - use the default value

0 - disable (TLS connections will not fail preemptively)

It can be changed also at runtime, via the RPC interface and config
framework. The config variable name is tls.low_mem_threshold1.

See also tls.low_mem_threshold2.

Example 1.32. Set low_mem_threshold1 parameter

...
modparam("tls", "low_mem_threshold1", -1)
...

Example 1.33. Set tls.low_mem_threshold1 at runtime

$ kamcmd cfg.set_now_int tls low_mem_threshold1 2048

9.26. low_mem_threshold2 (integer)

Sets the minimal free memory from which TLS operations on already established
TLS connections will start to fail preemptively. The value is expressed in KB.

The default value depends on whether the OpenSSL library used handles low memory
situations (openssl bug #1491).
As of this writing this is not true for any OpenSSL version (including 0.9.8e).

If an ill-behaved OpenSSL version is detected, a very conservative value is chosen,
which depends on the maximum possible number of simultaneously created
TLS connections (and hence on the process number).

The following values have a special meaning:

-1 - use the default value

0 - disable (TLS operations will not fail preemptively)

It can be changed also at runtime, via the RPC interface and config
framework. The config variable name is tls.low_mem_threshold2.

See also tls.low_mem_threshold1.

Example 1.34. Set tls.low_mem_threshold2 parameter

...
modparam("tls", "low_mem_threshold2", -1)
...

Example 1.35. Set tls.low_mem_threshold2 at runtime

$ kamcmd cfg.set_now_int tls low_mem_threshold2 1024

9.27. tls_force_run (boolean)

If enabled Kamailio will start even if some of the OpenSSL sanity checks fail (turn it on at your own risk).

If any of the following sanity checks fail, Kamailio will not start:

the version of the library the TLS module was compiled with is
"too different" from the library used at runtime. The versions should have the same major,
minor and fix level (e.g.: 0.9.8a and 0.9.8c are ok, but 0.9.8 and 0.9.9 are not)

the OpenSSL library used at compile time and the one used at
runtime have different Kerberos options

By default tls_force_run is disabled.

Example 1.36. Set tls_force_run parameter

...
modparam("tls", "tls_force_run", 11)
...

9.28. session_cache (boolean)

If enabled Kamailio will do caching of the TLS sessions data,
generation a session_id and sending it back to client.

By default TLS session caching is disabled (0).

Example 1.37. Set session_cache parameter

...
modparam("tls", "session_cache", 1)
...

9.29. session_id (str)

The value for session ID context, making sense when session caching is enabled.

By default TLS session_id is "sip-router-tls-3.1".

Example 1.38. Set session_id parameter

...
modparam("tls", "session_id", "my-session-id-context")
...

9.30. renegotiation (boolean)

If enabled Kamailio will allow renegotiations of TLS connection initiated by the client. This may
expose to a security risk if the client is not a trusted peer and keeps renegotiating, consuming CPU
and bandwidth resources.

By default TLS renegotiation is disabled (0).

Example 1.39. Set renegotiation parameter

...
modparam("tls", "renegotiation", 1)
...

9.31. config (string)

Sets the name of the TLS specific configuration file or configuration directory.

If set the TLS module will load a special configuration file or configuration files
from configuration directory, in which different TLS parameters can be specified on
a per role (server or client) and domain basis (for now only IPs). The corresponding
module parameters will be ignored if a separate configuration file is used.

If the file or directory name starts with a '.' the path will be relative to the
working directory (at runtime). If it starts
with a '/' it will be an absolute path and if it starts with anything
else the path will be relative to the main config file directory
(e.g.: for kamailio -f /etc/kamailio/kamailio.cfg it will be relative to /etc/kamailio/).

By default no TLS configuration file is specified.

The following parameters can be set in the config file, for each
domain:

tls_method

verify_certificate

require_certificate

private_key

certificate

verify_depth

ca_list

crl

cipher_list

server_name

server_id

The value for server_id can be any string, being used to match TLS
client config profile, overriding the match on ip:port and
server_name. This is the recommended way for selecting a specific
TLS client config profile, because the local or remote port is hard
to predict for a stream connection - see parameter
xavp_cfg to learn how to enable it.

All the parameters that take filenames as values will be resolved
using the same rules as for the tls config filename itself: starting
with a '.' means relative to the working directory, a '/' means an
absolute path and anything else a path relative to the directory of
the current Kamailio main config file.

Kamailio acts as a server when it accepts a connection and as a
client when it initiates a new connection by itself (it connects to
something).

9.32. xavp_cfg (string)

Sets the name of XAVP that stores attributes for TLS connections.

The following (inner) attributes can be set:

server_name - SNI to be used for outbound connections

server_id - string value to be used to match TLS config profile
for client (outbound) connections. If it is set, matching the TLS config
profile is done first on server_id and then on ip:port and server_name.
This is the recommended way for selecting a specific TLS client config
profile as the local or remote port is hard to predict for a stream
connection.

11. RPC Commands

11.1. tls.info

List internal information related to the TLS module in
a short list - max connections, open connections and the
write queue size.

Parameters:

None.

11.2. tls.list

List details about all active TLS connections.

Parameters:

None.

11.3. tls.options

List the current TLS configuration.

Parameters:

None.

11.4. tls.reload

Reload the external TLS configuration file (aka tls.cfg). It does not reload
modparam() parameters. Note that existing active TLS connections are not
terminated and they continue to use the old certificates. The new configuration
will be used for new connections.

Parameters:

None.

12. Status

12.1. License

Most of the code for this module has been released under BSD by
iptelorg. The GPL parts are released with an exception to link
with OpenSSL toolkit software components.

12.2. History

For version 3.1 most of the TLS specific code was completely
re-written to add support for asynchronous TLS and fix several
long standing bugs.